The Sensitivity of the End-On Shock Tube Detection Technique

Abstract

The sensitivity of an end‐on detection technique used to monitor light emission behind reflected shock waves is described. Using this detection method, emission from a test gas heated by a reflected shock wave is monitored through an observation window mounted in the end wall of the shock tube. The geometric factor of the end‐on detection system which relates the emission intensity within the test gas to the actual monitored intensity is derived and is shown to be constant under a number of experimental configurations. For the case of an exponentially growing emission signal, the sensitivities of the end‐on and more conventional side‐on detection techniques can be directly compared. For typical conditions encountered in studying the exponential growth of emission occurring during the C₂H₂+O₂ induction period, the end‐on detection system is shown to be 100 times more sensitive than a side‐on apparatus for experiments in which a detector with a small surface area is used (e.g., a liquid nitrogen cooled InSb ir detector). For detectors with large surface areas (e.g., photomultipliers with end windows), the end‐on technique is over 500 times as sensitive as side‐on methods.